One conventional type of infusion pump system employs a peristaltic pump in conjunction with an intravenous administration set. The set consists of flexible thermoplastic tubing through which fluid flows from a suspended container, such as a flexible bag or rigid bottle, to a patient's indwelling vein access device, such as a needle or cannula inserted into the patient. A length of the administration set tubing between the fluid container and the patient is mounted in the peristaltic pump which sequentially squeezes adjacent sections of the tubing so as to pump the fluid via a peristaltic action along the tubing into the patient.
Liquid medical products which are intended to be administered intravenously are typically stored in a central location in a hospital or other medical facility. Some such liquid products are typically stored in a refrigerator or cooler to preserve the product efficacy or to extend shelf life.
When a refrigerated liquid product is removed from storage and administered to a patient, the bulk of the liquid within the dispensing container or package typically remains relatively cold during the administration of the liquid patient. The administration tubing set through which the cold liquid flows also becomes cooler.
Conventional administration set tubing is molded from a polyvinyl chloride polymer, and the resiliency of this material decreases substantially with decreasing temperature. On the other hand, when the polyvinyl chloride polymer tubing is at normal room temperature, the tubing is much more flexible and resilient.
A peristaltic pump control system can be simply designed to provide a selected flow rate when operating at a constant speed with the tubing at a particular temperature (e.g., normal room temperature). When such a pump is operated on tubing at normal room temperature to squeeze and release a section of the tubing, the deformed tubing recovers to its original cross-sectional configuration relatively quickly. Thus, before that same section of tubing is subsequently squeezed again by the peristaltic pump, that section of tubing will be filled with substantially the same volume of liquid as was contained in the tubing during the prior pump stroke. Hence, a constant pump stroke rate relative to the section of tubing results in the pumping of constant flow rate of liquid through that section of tubing if the tubing temperature does not change.
However, if the temperature of the tubing decreases, the tubing becomes stiffer and less resilient. This can change the pumping characteristics. Consider the situation if a refrigerated, cold liquid is pumped through the tubing. When the peristaltic pump acts on a section of the cold tubing to first squeeze or deform the tubing into a closed configuration and then releases the tubing, the cold tubing will not recover to its original cross-sectional configuration as quickly as it would if it was at room temperature. Indeed, the tubing may not recover to its original cross-sectional configuration by the time the peristaltic pump again cycles to squeeze closed that same section of tubing. If the cold tubing has only recovered, say, about 75% of its full open cross-sectional configuration before being squeezed again by the peristaltic pump, then that section of tubing would contain substantially less liquid than if that tubing section had fully recovered to its original cross-sectional configuration prior to being subsequently squeezed by the pump.
Typically, peristaltic pumps are intended to supply a liquid through the administration set tubing at an adjustable, but constant rate. The rate may be adjusted to a selected rate over a range of rates. If a patient is supposed to receive, say, 10 milliliters per hour of liquid, then the peristaltic pump can be set to provide that flow rate based upon a pump operating speed which has been determined by the pump manufacturer for tubing at a constant temperature, typically a normal room temperature. If the temperature of the tubing differs from that used by the pump manufacturer in establishing the pump flow control system relationship between pump operating speed and flow rate, then the control system will not provide the desired flow rate when the tubing is at a higher or lower temperature.
Accordingly, it would be desirable to provide an improved system for regulating the fluid flow through a peristaltic pump. Such an improved system should accommodate variations in temperature, including variations in the temperature of the liquid product being administered to the patient as well as variations in ambient temperature.
Preferably, temperature sensing instrumentation used in such an improved system should also be protected from electrostatic discharge so as to eliminate, or at least minimize, the potential for damage to such sensors.